1. Field of the Invention
The present invention relates to a carbon nanotube field emitter array and method for fabricating the same and, more particularly, to a method that integrates a photomask into the structure of the carbon nanotube field emitter array for fabricating the carbon nanotube field emitter array.
2. Description of Related Art
The triode structure of a carbon nanotube field emission display (CNT-FED) is shown in FIG. 1. The triode structure has the characteristics or advantages of high electron energy, increased illumination efficiency, and low controlling voltage. In the triode structure, the anode electrode increases the energy of the electron, the cathode electrode acts as an electron emitter, and the gate electrode is responsible for drawing the electrons out of the cathode electrode. Currently, the carbon nanotube powder is first mixed with the organic materials to form a paste, which is then coated on a substrate and patterned by screen-printing to form the CNT emitter array of a CNT-FED. However, the size of the CNT emitters formed by the aforesaid method is restricted. Accordingly, the photolithography process may be a preferred method to pattern the CNT emitter array because it is less restricted in the size of the CNT emitters and can control the distance between the CNT emitters and the gate electrode easily, thereby lowering the required driving voltage thereof. However, that leads to another problem of how to carry out the photolithography process in the fabrication of the CNT emitter array successfully.
Generally speaking, the photolithography process uses an independent photomask for patterning an object, so it needs an extremely precise alignment between the photomask and the object when the photolithography process is carried out. However, during the manufacturing of the CNT-FEDs, it is required to carry out a high temperature process, which will cause shrinkage or deformation of the substrate, and therefore raises the difficulty of alignment of the photolithography process.
Currently, the CNT emitter array of the triode structure of a CNT-FED is patterned through obverse exposure of the photosensitive CNT layer, as shown in FIG. 2. On a substrate 10, a cathode layer 20, a dielectric layer 30, and a gate layer 40 are formed in turns. In the meanwhile, a dielectric hole and a gate hole are formed at the same location to expose the cathode layer 20. Afterwards, a CNT layer is coated on the entire top surface of the substrate 10 and then patterned by the photomask 60 to form the CNT emitter 50′ on the exposed cathode electrode 20. However, it is necessary to align precisely and repeatedly during the current photolithography process. If the alignment is deviated, a short circuit will easily occur between the cathode layer and the gate layer of the CNT emitter.
To resolve the aforementioned problem, a method of manufacturing a triode carbon nanotube field emitter array is disclosed in US patent application publication 2002/0094494 A1 by Samsung SDI. The method teaches that a transparent hole is formed between a transparent electrode and a metal electrode. The transparent hole is then filled with the CNT paste and patterned by the reverse exposure to form a CNT field emitter. However, such a structure makes the gate electrode act inefficiently on the CNT emitter.
Therefore, it is desirable to provide an improved carbon nanotube field emitter array and method for fabricating the same to mitigate and/or obviate the aforementioned problems.